1. Field of the Invention
The present invention relates to the field of Data Communication. More specifically, the present invention relates to data circuit terminating equipments (DCEs) such as modems for transmitting voice and data over analog-loop telephone lines.
2. Background Information
Current DCEs that support transmission of both voice and data over a single analog-loop telephone line typically implement the support in one of two approaches. Under the first approach, a DCE operates in one of two switchable modes, a voice mode and a data mode, whereas under the second approach, a DCE operates in a single continuous combined voice and data mode.
More specifically, under the first approach, both the call originating and call responding DCEs start out in the voice mode, where analog voice signals are bypassed from the transmitting telephone coupled to one of the DCEs onto the analog-loop telephone line, and similarly from the analog-loop telephone line to the receiving telephone coupled to the other DCE. While the DCEs are in voice mode, no data are transmitted by the DCEs on behalf of data transmitting equipments (DTEs), such as computers, coupled to the DCEs at both end of the connection. To switch into the data mode, one of the DTEs would cause its DCE to transmit a predetermined signal pattern on its behalf. Upon detection of the predetermined signal pattern, the other DCE would acknowledge. If the acknowledgment is received by the initiating DCE within a predetermined time period, the DCEs would jointly establish a data transmission protocol, enter the data mode, and mute the DCE's voice path. The DTEs can now transmit data to each other through their respective DCEs and over the analog-loop telephone line. At the end of data transmission, the DTE that initiated the mode switching would cause its DCE to transmit another predetermined signal pattern on its behalf, return to the voice mode, and unmute the voice path. Likewise, upon detection of this other predetermined signal pattern, the other DCE would also forward the signal to its DTE, return to the voice mode, and unmute the voice path. Voice signals are once again bypassed from the transmitting telephone onto the telephone line, and from the telephone line to the receiving telephone.
Under the second approach, the DCEs always operate in a single continuous combined voice and data mode. The DCEs jointly establish a data transmission protocol at start up. The analog voice signals received from the coupled telephones are digitized by the DCEs or forwarded to the coupled DTEs for digitization. The DCEs transmit the digitized voice signals intermixed with the data received from the coupled DTEs. Conversely, the digitized voice signals received from the analog-loop telephone line are converted back into analog voice signals by the DCEs or forwarded to the coupled DTEs for conversion. The DCEs then forward the analog voice signals to the telephones.
The first approach has the disadvantage that there is no voice communication between the connected parties during data transmission. Thus, DCEs implementing the first approach are really suitable only for applications where voice communication is unnecessary during data transmission or data transmission is merely required intermittently and for short durations.
The second approach has the disadvantage that the DCEs on both ends of the connection must support continuous combined voice and data mode. Therefore, for applications frequently involving "unacquainted" users, an initial phone call using "standalone" telephones directly coupled to another analog-loop telephone line must be made to establish the fact that such continuous combined voice and data call can be made between two DCE coupled telephones. Thus, DCEs implementing the second approach are really suitable only for applications involving primarily "acquainted" users.
With the continuing increase in the capabilities of microprocessor based desktop computers, they are being applied to more and more applications that require simultaneous voice and data communications between two users. A particular example of these applications is personal conferencing where users at different sites cooperate orally and interactively with a shared workspace application on the creation or review of documents. Another example is remote technical support where the support engineers communicate orally with the users as well as interacting remotely with programs executing on the users' systems for diagnostic or demonstration purposes. Due to the disadvantages discussed above, neither types of DCEs serve these applications well. As a result, most users of these applications resort to two telephone lines, with one dedicated for voice communication, and the other dedicated to data communication.
Thus, it is desirable to be able to support voice and data communication between two users over a single analog-loop telephone line in a more flexible and user friendly manner. As will be disclosed in more detail below, the present invention provide for such method and apparatus that advantageously achieves these and other desirable results.